EP1720690B1 - Multilayer dose and process for producing the same - Google Patents

Abstract

A dose of multilayer synthetic resin for the realization of multilayer objects by compression molding, said dose having an axis of symmetry and comprising a first synthetic resin (2) and at least one fine functional layer (3) of synthetic resin forming the outer shell of a body of revolution defined about said axis of symmetry, said body of revolution comprising two ends disposed in a direction parallel to the axis of symmetry, said dose being characterized in that the functional layer (3) is imprisoned in said first synthetic resin (2), totally or in such a way that no more than a single one of said ends is not imprisoned in said first resin (2).

Description

Field of the invention

The present invention relates to a method for producing multilayer objects according to claim 5 by compression molding a multilayer dose according to claim 1.

The present invention also relates to methods for the manufacture of a multilayer dose according to claims 6 and 8.

State of the art

Multilayer objects obtained by compression molding a multilayer dose are described in particular in the following patent documents: FR-A-2 520 288 ; EP-A-1 208 955 ; FR-A-2 180 831 ; JP-A-60259425 and US-2003/080461 .

The patent US 4,876,052 describes a multilayer dose ( figure 1 ) characterized in that a functional resin 3 is completely trapped inside a synthetic resin 2. The functional resin and the outer resin are of different nature. For example, the functional resin has high gas barrier properties, while the resin forming the outer layer is chosen for its mechanical and hygienic properties. These multilayer doses make it possible to obtain multilayer objects by compression molding said dose. However, the objects obtained according to the method described in the patent US 4,876,052 require a large proportion of functional resin in the object; which generates two major disadvantages; the former being a prohibitive cost and the second a resistance to mechanical stress diminished. The absence of adhesion between the functional resin and the external resin reduces the solidity of the object and creates a risk of cohesion of the outer layer. Another disadvantage of the patent US 4,876,052 lies in the fact that we can only slightly adjust the respective amount of resins 2 and 3. As will be shown later in the disclosure of the invention, these quantities are fixed by the geometry of the object and by the flows during compression of the dose.

The Japanese patent JP 2098415 proposes to make a multilayer object by compression molding starting from a composite dose ( figure 2 ) characterized in that the synthetic resin 2 covers only the lateral faces of the functional resin 3. The compression molding of this dose along its axis of symmetry leads to an object having a multilayer structure characterized in that the synthetic resin 2 partially traps the functional resin 3. However, the multilayer objects made from two resins according to the patent JP 2098415 have two major disadvantages; the first being to have the functional resin 3 exposed in the central surface of the object on at least 10% of the total surface of the object; and the second being to require an amount of functional resin 3 in the subject of at least 30% of the total amount of resin. This leads on the one hand to objects having a prohibitive cost, and on the other hand to objects with highly modified mechanical properties mainly in the center of the object. Another disadvantage of the patent JP 2098415 lies in the fact that we can only slightly adjust the respective amount of resins 2 and 3, these quantities being fixed by the geometry of the object and the flows during the compression of the dose.

It is proposed in the patent JP 2098415 to use a dose according to the preamble of claim 1 comprising 3 layers to remedy in part the aforementioned drawbacks ( figure 3 ). This dose consists of a first resin 4 forming the central part of the dose, a functional resin 3 covering only the lateral faces of the first resin, and a third resin 2 covering only the lateral faces of the functional resin . The crushing of this composite dose along its axis of symmetry leads to a multilayer object. The use of a tri-layer dose has the advantage of reducing the amount of functional resin 3 used and leads to objects having weakly modified mechanical properties compared to the same object comprising a single resin 2. This method makes it possible to add an adhesive layer between resins of different types; therefore the cohesion and strength of the object is improved. However, the functional resin 3 does not cover the central part of the multilayer object which leads to objects without barrier property close to the axis of symmetry over an area of at least 10% of the surface of the object. This central zone of the object not covered by the barrier resin layer 3 reduces the barrier performance of the object and makes this solution less efficient.

The patent application CH01619 / 04 describes multilayer objects made from a multilayer dose ( figure 4 ) compression molded. The objects described in this patent application have a multilayer structure characterized by the position of the functional layer forming a double zigzag-shaped fold. The functional layer is correctly distributed throughout the object, even in the central part. The method of producing multilayer objects described in the patent application CH01619 / 04 also allows to control the thickness of the functional layer. An adhesive layer may be added between the resin forming the surface of the object and the functional resin. However, the compression of the dose requires a method and a specific molding device. This method requires in particular additional tooling movements compared to the basic compression process setting relative movement of the two parts of the mold. In the case of high-speed molding, it may be disadvantageous to use a compression device as described in the patent application. CH01619 / 04 .

Object of the invention

The present invention makes it possible to produce multilayer objects by compression molding by remedying the aforementioned problems. This method makes it possible in particular to use a compression device without modification with respect to the device used to produce monolayer objects.

Summary of the invention

The invention consists of a multilayer dose having an axis of symmetry for producing multilayer objects by compression molding, consisting of a first synthetic resin and a thin functional layer trapped in said first resin; said functional layer representing less than 20% of the volume of the dose; the multilayer dose being characterized in that the functional layer forms the envelope of a body of revolution about the axis of symmetry and in that the distance of the layer to the axis of symmetry is variable.

Detailed description of the invention

The invention will be better understood hereinafter by means of a detailed description of the examples illustrated by the following figures.

Brief description of the figures

• The Figures 1 to 4 describe the multilayer doses described in the prior art for producing multilayer objects by compression molding.
• The figure 1 shows a bilayer dose made according to the patent US 4,876,052
• The figure 2 shows a bilayer dose used in the patent JP 2098415 .
• The figure 3 illustrates a dose comprising 3 layers described in the patent JP 2098415 .
• The figure 4 shows an annular multilayer dose described in the patent application CH01619 / 04
• The figure 5 shows a multilayer dose according to the general concept of the invention.
• The figure 6 illustrates the flow of material and the velocity profile during the compression of the dose.
• The figure 7 illustrates the compression of a dose as described in the patent JP 2098415 as well as the multilayer object obtained.
• The figure 8 shows the limits of the multilayer objects obtained according to the patent JP 2098415 .
• The Figures 9 to 20 examples of multilayer doses, their methods of implementation and an example of a device that can be used.
• The figure 9 illustrates a first example of a dose corresponding to the invention.
• The figure 10 shows the multilayer object obtained after compression of the dose described on the figure 9 .
• The figure 11 shows a dose made according to the invention and comprising 5 layers.
• The Figures 12a and 12b illustrate annular doses forming part of the invention.
• The figure 13 presents a multilayer object obtained from the compression of the dose presented on the figure 12a .
• The figure 14 is another example of a dose forming part of the invention.
• The Figures 15 to 19 describe methods for performing doses as described in figures 9 , 11 , 12 and 14 .
• The figure 15 illustrates a first method of producing doses in which the flow rate of one of the layers varies periodically.
• The figure 16 shows a second method of producing doses in which the flow rate of two layers varies periodically and in phase opposition.
• The figure 17 illustrates a multilayer rod used for the production of multilayer doses and can be performed with the described embodiment figure 16 .
• The figure 18 illustrates a third method of producing multilayer doses according to which the flow rate of all the layers varies periodically and with an overall flow rate having small variations.
• The figure 19 shows another method of producing multilayer doses according to which the flow rate of each layer varies periodically and according to which the overall flow rate is periodically zero,
• The figure 20 illustrates a device for performing multilayer doses according to the invention.
• The Figures 21 to 27 illustrate another example of multilayer doses, an embodiment and a device.
• The figure 21 shows another type of multilayer dose corresponding to the invention.
• The figures 22 shows the multilayer object obtained from the compression of the dose described on the figure 21 .
• The Figures 23a to 23d illustrate the method of performing the dose described on the figure 21 .
• The Figures 24a to 24c show a method for transferring the dose into the compression mold.
• The Figures 25a to 25c illustrate the compression of the dose in the compression device.
• The figure 26 shows the general concept of a device that can be used for the production of multilayer doses.
• The figure 27 shows a device for producing doses represented on the figure 21 .

Detailed description of the figures

The invention consists in producing multilayer doses according to the concept shown figure 5 . This dose consists of a first synthetic resin forming the dose and at least one second resin trapped in the first resin and forming a thin layer whose distance to the axis of symmetry R and the thickness E varies as a function of the position on the axis of symmetry z. This type of dose makes it possible to jointly optimize the position of the barrier resin layer in the molded article, as well as the thickness of this layer.

In order to better understand the interest of the dose described above, it is necessary to consider the flow of the resins during the compression of the dose ( figure 6 ). This flow depends mainly on the rheological properties of the resins during the compression as well as the geometry of the object. The figure 6 shows that this flow is faster halfway between the walls than near the walls of the tooling. In the vicinity of the tooling walls, the speed of movement of the particles tends to zero, but the shear deformation is high. Conversely, halfway between the walls the particle velocity is maximum and shear deformation is minimal. During flow, the functional resin layer is driven and deforms non-uniformly depending on its position in the flow profile. Thus, the final position of the functional resin layer in the object is determined by the initial position of the functional layer in the dose and the sum of the deformations experienced during the flow.

The Figures 7a to 7c illustrate the compression of a dose as proposed in the patent JP 2098415 to demonstrate the limits of the multilayer objects obtained by this method and better understand the object of the present invention. The figure 7a shows a tri-layer dose made according to the patent JP 2098415 . This dose comprises a first resin 4 forming the central part of the dose, a functional resin 3 covering only the lateral faces of the first resin, and a third resin 2 covering only the lateral faces of the functional resin. This dose has a height called H1, an outside radius R1, and a radial position of the functional layer R. The compression of this dose leads to an illustrated intermediate step figure 7b . The figure 7b shows the deformation of the functional layer in the partially compressed dose. It is important to note that this layer deforms towards the periphery of the object, ie in the direction of the flows; which implies that the central part of the object can not be covered by the functional layer. It is interesting to note also that in the intermediate stage the functional layer is still distant from the material front; which indicates that the object obtained in the intermediate step does not exhibit barrier properties at the periphery. The Figure 7c illustrates the object obtained after compression of the dose. The functional layer 3 has propagated to the end of the object while remaining encapsulated at the periphery of the object. As shown in Figure 7c , the functional layer did not propagate in the central part of the object. The object obtained according to this method therefore has the disadvantage of not having barrier properties at its center.

Objects as represented on the Figure 7c were made from doses as illustrated figure 7a . The experimental results have been reported on the figure 8 . The surface of the object is denoted Sp; the central surface of the multilayer object not covered by the functional layer is denoted S; the thickness of the object is denoted E, the thickness of the dose is denoted H1. The ratio H1 / E represents the compression ratio. The figure 8 shows how the surface fraction not covered by the functional layer S / Sp varies as a function of the compression ratio H / H1. The ratio S / Sp is greater than 10% even for compression ratios of 20. This result indicates that the functional layer covers in the best case 90% of the surface of the object. The measurement of the barrier properties on an object having 90% of its surface covered by the functional material shows that this object is at least 10 times less impermeable to gas than the same object made according to the invention and having 100% of its surface area. covered by the functional layer. These results were obtained using a functional resin 100 times more impermeable than the base resin.

The figure 9 shows a first example of a multilayer dose corresponding to the invention. This dose comprises a first layer of resin 4 encapsulated in a functional resin layer 3, said functional resin layer 3 itself being encapsulated in a resin layer 2 forming the outer surface 5 of the dose 1. The ends 7 and 7 ' of the functional layer are each joined in 1 point so that the layer 4 is totally trapped in the functional layer 3. The position of the functional layer in the dose allows after compression to cover 100% of the surface of the object, c ie the periphery and the center. This leads to a position of the functional layer in the dose according to a profile as illustrated figure 9 forming a kind of pocket closed at both ends 7 and 7 'and forming a belly 10 located about halfway up the dose. The radial position of this belly is not random, it is fixed by the geometry of the object and that of the dose. The exact radial position of the belly 10 propagates the layer to the periphery of the object and ensures that the functional layer remains encapsulated in the object. The experiments showed that the radial position of the belly of the functional layer in the dose was a function of the compression ratio, the geometry of the object, and the rheology of the resins.

An example of a multilayer object obtained from the compression of this dose is illustrated figure 10 . This object has the particularity of having a double layer of functional resin covering the entire surface of the object. This object is obtained by compressing the multilayer dose in a simple compression device that does not require modification with respect to the compression device that would be used to produce the same object from a monolayer dose. A detailed observation of the multilayer object at the axis of symmetry as illustrated figure 10 shows the ends 7 and 7 'of the functional layer forming a kind of peak perpendicular to the surface of the layer.

The figure 11 shows that the invention is not limited to a tri-layer dose as illustrated figure 9 . A dose comprising 5 layers as illustrated figure 11 is particularly advantageous because the insertion of an adhesive layer 3b and 3c on either side of the barrier layer 3a makes it possible to combine resins of different types while guaranteeing good adhesion between the different layers, which avoids the possible delamination or decohesion problems in multilayer objects. The adhesive and barrier layers are parallel and in small quantities. The set of adhesive layers 3b and 3c and the barrier layer 3a forming the functional layer 3 generally represents an amount of resin less than 15% of the total volume of resin forming the dose, and preferably an internal amount of 10%.

The Figures 12a and 12b show that the invention is not limited to cylindrical doses as illustrated figure 9 ; these doses may be annular in order to produce multilayer objects having an orifice. The multilayer annular doses as represented figure 12a and 12b are particularly advantageous for producing multilayer objects having an orifice such as tube heads. The dose presented on the figure 12a is used when the compression of the dose causes a joint flow to the periphery and to the center; while the dose 12b is used when the compression of the dose only gives rise to a flow towards the periphery.

The figure 13 shows a tube head made by compression molding a multilayer dose as shown figure 12a . We find in the thickness of the object a functional double layer covering the entire surface of the object. The functional layer propagates to the periphery of the object and to the orifice while remaining fully encapsulated. In order to control the propagation of the layer in both directions, it is necessary to adjust the geometry and position of the functional layer within the dose.

Doses similar to the doses presented figures 9 and 12 can be realized. The figure 14 shows a multilayer dose comprising a layer of resin 4 trapped laterally by a thin layer of functional resin 3, it even trapped by a layer of resin 2 forming the outer surface 5 of the dose. The functional resin layer 3 defines an axially symmetrical axisymmetric geometry at both ends; the radius Rmin defining the opening at the ends being less than or equal to 80% of the maximum radius Rmax defining the belly of the functional layer; and preferably Rmin is less than 10% of the radius Rmax. The dose presented figure 14 differs singularly from the dose proposed in the patent JP 2098415 ( figure 3 ) characterized in that the functional resin layer forms a cylindrical geometry. The extrusion of doses as described in the patent JP 2098415 can lead to a geometry of the functional resin layer that is not perfectly cylindrical as on the figure 3 but which is slightly distorted. This slight deformation of the functional layer can be caused naturally; by a joint effect of stress relaxation at the extruder outlet (swelling phenomenon), and gravity which creates a slump of the dose under its own weight. These deformations of the dose can lead to a geometry of the functional layer characterized by a minimum radius Rmin greater than 80% of the maximum radius Rmax. As it has been demonstrated previously, this type of dose does not lead to multilayer objects having high impermeability properties due to the surface not covered by the functional layer in the center of the object. The invention improves the impermeability of multilayer objects by significantly increasing the surface of the object covered by the barrier layer. As will be explained below, the production of multilayer doses as presented figure 14 requires a specific device and can not be realized according to the method presented in the patent JP 2098415 .

The method for producing multilayer objects described below is particularly advantageous for producing objects such as plugs, lids, preforms or tube shoulders. This method can also be used advantageously to produce preforms in the form of slabs; these wafers are then used in thermoforming or blowing thermoforming to form multilayer objects.

The doses presented figures 9 , 11 , 12 and 14 can be carried out according to several methods. These different methods have one thing in common: coextruding the resins to form a multilayer structure; and at least the resin forming the central layer 4 of the multilayer structure is extruded with a variable flow rate.

A first method of performing doses is illustrated figure 15 . This method makes it possible to produce multilayer doses corresponding to the type of dose presented figure 14 . This method consists in continuously co-extruding a multilayer rod as presented figure 15 . The flow rate of the layer 2 forming the outer surface of the dose, and the flow rate of the functional layer are constant. On the other hand, the flow rate of the layer 4 forming the internal layer of the dose varies periodically between a maximum and a minimum value. The periodicity of the flow variations defines a wavelength corresponding to the length of the dose and also defines the cutting frequency of the multilayer rod. This method is particularly advantageous for producing multilayer doses at a very high rate. The illustrated method of production figure 15 also makes it possible to produce doses having the layer 4 completely encapsulated in the functional resin 3. For this, the resin layer 4 must have a flow rate varying periodically between a maximum flow rate and a zero flow rate.

A second method of performing doses is illustrated figure 16 . This method differs from the illustrated method figure 15 in that the flow rate of the resin layers 2 and 4 varies periodically and in phase opposition so that the overall flow rate remains constant or varies slightly. The flow rate of the functional layer remains constant. The multilayer rod is cut off at the output of the coextrusion device at the frequency set by the periodic variations in the flow rate of the layers 2 and 4. This method can be advantageous in order to avoid defects related to too abrupt variations in the overall flow rate (instabilities of extrusion, orange peel ...). The variations in the flow rate of the layers 2 and 4 at the output of the coextrusion device are generally progressive, even if the control signal is in the slot as indicated on FIG. figure 15 . This phenomenon is linked to the inertia of the resin in the device. It is also possible to control the flow variations in a progressive manner using appropriate devices.

The figure 17 illustrates a multilayer rod that can be obtained according to the described method figure 16 . The cutting of this multilayer rod periodically at the output of the coextrusion device makes it possible to obtain multilayer doses. The multilayer rod is obtained by extruding the functional layer with a constant flow rate and by extruding the resin layers 2 and 4 with a periodically varying flow rate and in phase opposition. The flow rate of the resin layer 4 varies periodically between a maximum flow and a zero flow, which leads to a total encapsulation of the resin layer 4 within the functional resin layer.

The figure 18 illustrates the method of producing multilayer doses identical to that presented figure 9 . This method consists in co-extruding a multilayer rod comprising a resin layer 4, a functional layer 3 and a resin layer 2 forming the outer surface of the rod. The flow rate of the resin layers 2 and 4 varies periodically and in phase opposition. The flow rate of the resin 2 forming the outer layer of the ring varies between a minimum and maximum value periodically. The flow rate of the functional layer 3 varies periodically and has a value of zero during a period t1. The flow rate of layer 4 also varies periodically and has a value of zero during a period t2. The variation of the flow of the layers is done at a frequency, corresponding to the frequency of production of the doses. During the period t2, only the outer layer 2 is extruded, during the time (t2-t1), only the layers 2 and 3 are extruded.

Another method of producing multilayer doses as illustrated figure 14 consists of a discontinuous coextrusion process, characterized in that the overall coextruded resin flow rate varies between a maximum value and a zero value; the quantity of material dosed during a period corresponding to a dose. This method of realization is illustrated figure 19 . For a time t1, the overall coextruded flow rate is zero, and for a period t2-t1 only the layers 2 and 3 are extruded, which makes it possible to encapsulate the layer 4 inside the layer The method of producing multilayer doses according to method 19 has the advantage of allowing a volumetric dosage of the multilayer dose, thus a greater regularity of the doses.

The invention is not limited to a method for producing multilayer doses comprising 3 layers. For example, for the production of doses comprising 5 layers as illustrated figure 11 , a piloting method similar to the illustrated method figure 18 can be used.

Similarly, the invention is not limited to methods for producing cylindrical doses; annular doses, for example, which can be carried out.

Several devices can be used to produce multilayer doses according to the illustrated method Figures 15 to 18 ; these methods of co-extruding a rod or multilayer pipe and varying the flow rate of one or more layers periodically; the rod or multilayer tube is then cut periodically to form the doses. The device comprises at least one coextrusion head connected to several extruders in order to feed the molten resins into the coextrusion head, and means for periodically varying the flow rate of one or more layers.

The figure 20 illustrates an example of a device for producing multilayer doses. This device comprises channels 11, 12 and 13 for the respective supply of the resins 2, 3 and 4; the resin 3 forming the functional layer, and the resins 2 and 4 respectively forming the outer and inner layers of the dose. The channels 11, 12 and 13 are connected to the extruders via appropriate known means. The device also comprises a splitter 14 for appropriately distributing each layer on the circumference. Several types of splitters can be used such as spiral splitters or cardioid geometry distributors or coat rack. The device comprises a tip 15 which makes it possible to modify the geometry of the rod or the extruded tube by changing the geometry of the tip. The device will preferably have a common junction 16 of the resin layers 2, 3 and 4.

This common junction 16 allows an easy variation of the position of the functional layer 3 by varying the respective flow rates of the layers 2 and 4. The device is characterized by means 17 and 18 for periodically varying the flow rate of the resin layers 2 and 4. The reciprocating movement of the pistons 17 and 18 allows a rapid and periodic variation of the flow rate of the layers 2 and 4. A downward movement of the piston creates a rise in pressure and consequently an increase in the flow rate of the layer. Conversely, a rise of the piston creates a decrease in pressure and decreases the flow rate of the layer. For greater efficiency the piston can be associated with one or two shutters, the first being located upstream and the second downstream of the piston. The piston can be actuated mechanically, or via a jack. The invention is not limited to the device described above. Pistons and shutters may also be associated with the functional layer 3. A device similar to that described figure 20 can be used to achieve a dose comprising 5 layers.

The figure 21 illustrates another multilayer dose particularly advantageous for producing multilayer objects by compression molding. This dose comprises a first layer of resin 4 forming the internal part of the dose; a thin layer of functional resin encapsulating the resin layer 4, and a resin layer 2 forming the outer layer of the dose and encapsulating the functional resin layer 3. The functional layer 3 defines a three-dimensional axisymmetric shape in the shape of a pear; and has an end 7 located near the axis of symmetry forming a small, slightly conical opening. Layer 3 intersects the axis of symmetry at a point opposite said end 7.

These multilayer doses are particularly advantageous for forming multilayer objects by compression molding said dose in a mold. The figure 22 shows a multilayer object made from the dose represented figure 21 . This object comprises a functional double layer 3a and 3b trapped in the wall of the object; said functional layer having a discontinuity at the axis of symmetry of the object. This discontinuity present as a small diameter hole in the functional layer 3b of the object. This hole corresponds to the end 7 of the functional layer 3. The diameter of said hole in the functional layer 3b is less than a value of 10 mm and is generally less than 3 mm. The multilayer object 22 obtained from the dose represented figure 21 , has a first layer 3a completely absent from the surface of the object, and a second layer 3b having an opening and optionally present on the surface of the object. For reasons of hygiene and performance of the multilayer object 22, it is preferable that the layer 3b is not on the side of the surface of the object in contact with the packaged product.

The invention is not limited to a dose having 3 layers as on the figure 21 . It may be advantageous to have a higher number of layers, especially in order to improve the adhesion between the layers. In this sense, the functional layer 3 presented figure 21 can be considered as a set of several thin parallel layers. For example, the functional layer may itself contain 3 layers including a barrier resin layer sandwiched between two layers of adhesive resins.

The method of producing multilayer doses represented figure 21 is illustrated figure 23a to 23d . This method consists in molding the multilayer doses and is characterized in that the resins are fed sequentially into a variable cavity of a transfer mold 19; the volume of the cavity varying with the amount of resin fed into said cavity. These doses are then transferred to the molten state in the compression mold in order to produce the multilayer object. The figure 23a shows the transfer mold 19 before filling the resins. The sheath 20a, the piston 20b and the cover 21 constitute the transfer mold 19, and define a cavity, having an opening created by the orifice 22. Before supplying the resins, the volume of the cavity is reduced. The method consists in first supplying the resin 2 forming the outer layer of the dose. The figure 23b shows the resin 2 supplied by the orifice 22, causing the displacement of the piston 20 and jointly inducing an increase in the volume of the proportional transfer mold cavity 19 to the volume of resin fed. The method consists of feeding the functional resin 3 into the transfer mold 19. figure 3c shows the supply of the resin 3 and its propagation inside the resin 2 already in the mold. The method finally consists in feeding the resin 4 forming the inner layer of the dose. The figure 3d illustrates the supply of the resin 4 and its propagation inside the functional layer 3 together with the displacement of the piston 20.

The molten multilayer dose is then transferred from the transfer mold to the compression mold. The transfer method is briefly illustrated from the Figures 24a to 24c . The first step of this illustrated method figure 24a consists in separating or opening the lid 21 at the surface with the lower surface of the multilayer dose. The dose is then expelled from the transfer mold 19 via the piston 20b as illustrated. figure 24b . The figure 24c shows the multilayer dose deposited in the cavity of the compression mold 23.

The multilayer dose must be in the molten state as it is transferred into the compression mold 23 to allow compression molding and avoid appearance defects. For this, the control of the temperature of the transfer mold 19 and the residence time of the dose in the transfer mold is very important. The temperature of the parts constituting the transfer mold 19 must be adjusted, in order to jointly allow the release of the dose and the formation of a skin on the surface of the dose sufficiently fine to remelt before compression. The temperature of the transfer mold must be as high as possible in order to approach the temperature of the molten resin, and the residence time in the transfer mold must be as short as possible.

The ejection of the multilayer dose into the compression mold can be done by another method than that illustrated figure 24 . For example, a lateral opening of the sheath 20a perpendicular to the axis of symmetry allows easier extraction of the dose.

The Figures 25a to 25c illustrate the compression of the multilayer dose. The figure 25a shows the positioning of the dose in the mold cavity 23. The figure 25b shows the descent of the punch 24 which compresses the dose and forms the multilayer object. The figure 25c illustrates the multilayer object obtained.

A device for producing multilayer objects from a molded dose is presented schematically figure 26 . This device consists of a first carousel 25 including molds, means for compression doses and means for ejection of molded objects. This device also consists of a second carousel comprising the transfer molds 19, means for supplying the resins sequentially in the transfer molds, means for increasing the volume of the cavity of the transfer molds during the filling of the resins in said molds, and also ways to transfer the doses into the compression molds. The transfer of the doses is at the meeting point 27 of the trajectory of the transfer molds and the compression molds. The device further comprises means for rotating the carousels and means for regulating and controlling the parameters.

The description of the transfer carousel 26 is illustrated figure 27 . This rotating carousel carries transfer molds 19. During the rotation of the carousel 26, the molds 19 pass sequentially over a first feed groove 28, a second feed groove 29 and a third groove The feed grooves 28, 29 and 30 are fixed and are connected to extruders. When the transfer mold 19 passes right of a groove, the resin fed under pressure into the groove fills the cavity of said mold. The figure 27 indicates that a mold passing sequentially over the grooves 28, 29 and 30 fills sequentially resins fed into the respective grooves. Thus, by supplying the resins 2, 3 and 4 respectively in the grooves 28, 29 and 30, a dose identical to that presented on FIG. figure 21 . The respective quantities of resins fed into the cavity of the transfer mold 19 can be adjusted with the lengths respective L1, L2 and L3 grooves 28, 29 and 30 and with the supply pressure of each resin.

The objects made according to the invention have particularly advantageous barrier properties. This can be explained in part by noting that most objects made according to the invention have a functional layer sufficiently covering the surface of the object and in particular the surface close to the axis of symmetry of the object.

The resins used in the context of the invention correspond to the thermoplastic resins commonly used, and more particularly those used in the packaging sector. Among the barrier resins that can be used to form the functional layer 3, mention may be made of ethylene vinyl alcohol copolymers (EVOH), polyamides such as nylon-MXD6, acrylonitrile methyl acrylate copolymers (BAREX), fluoropolymers such as PVDF. Also some resins that can be used for layers 2 and 4 of the dose: polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), polyester (PET). This list is not exhaustive. When choosing resins, it is important to select products with similar viscosities. In general, it is preferable to use resins which at the working temperature have a viscosity ratio of less than 10, and preferably a viscosity ratio of less than 3 will be selected.

The invention also relates to multilayer doses comprising a plurality of functional layers; said functional layers being individually trapped in a resin forming at least 80% of the volume of said dose. According to the invention at least one functional layer has a distance to the axis of symmetry that varies. The use of a dose comprising several functional layers can be advantageous at a very high rate of production. Indeed, at very high rates, it is difficult to obtain large variations in flow. The second functional layer may be of tubular geometry centered on the axis of symmetry of the dose; the radial position of this layer in the dose being such that the compression of the layer leads to a multilayer object having two independent functional layers which overlap partially and lead to properties similar to those of a continuous layer. The second functional layer may also have a distance to the variable axis of symmetry. A particularly interesting dose has its two parallel functional layers.

The invention is particularly interesting for producing multilayer objects such as preforms or plugs.

In the examples presented here, the doses and the objects are of simple geometry, but it goes without saying that the invention concerns any dose and object geometry.

The objects obtained according to the invention comprise a functional layer 3 forming at least one fold at the periphery of the object. Objects also having a second fold close to the axis of symmetry of the object can be obtained. An arrangement of the zigzag functional layer can be obtained in the object.

The invention has been described with a single functional layer 3 distributed in the dose. Doses comprising a plurality of functional layers 3 may also be used; said functional layers being all centered on the axis of symmetry of said dose. The multilayer objects obtained are characterized in that the functional layers overlap at least partially, and are distributed throughout the object.

Other dose geometries can be used. It has been observed that doses having a part of their concave surface are particularly advantageous. Such dose geometries facilitate a good distribution of the functional layer in the multilayer object.

The production of packaging or packaging components for food uses requires high hygiene properties. It is thus often desirable that the functional layer 3 is not in direct contact with the packaged product. It may be advantageous to completely enclose the functional layer 3 in the dose, so that said functional layer is completely trapped in the object.

Alternatively, only one end of the barrier layer may not be trapped.

Claims (8)

1. A multilayer dose (1) having an axis of symmetry for the realization of multilayer objects by compression molding, constituted by a first synthetic resin (2) and by a thin functional layer (3) imprisoned in said first resin (2), said functional layer (3) representing less than 20% of the volume of the dose (1), characterized in that the functional layer (3) forms the shell of a body of revolution about the axis of symmetry and in that the distance from the functional layer (3) to the axis of symmetry is variable.
2. The dose (1) as claimed in claim 1, characterized in that the ratio (Rmin-R0)/(Rmax-R0) is less than 0.8, Rmax and Rmin being respectively the maximum and minimum distances from the functional layer (3) to the axis of symmetry and R0 being the radius of an orifice centered about the axis of symmetry, the value of R0 conforming to the following relationship: 0 ≤ R0 < Rmin.
3. The dose (1) as claimed in either one of the preceding claims, characterized in that the functional layer (3) itself forms a multilayer structure (3a, 3b, 3c) comprising a layer of barrier resin (3c) imprisoned between two layers of adhesive resin (3a, 3b).
4. The dose (1) as claimed in one of the preceding claims, comprising a plurality of functional layers.
5. A multilayer object obtained by compression molding of a multilayer dose (1) having an axis of symmetry, said dose (1) being constituted by a first synthetic resin (2) and by a thin functional layer (3) imprisoned in the first resin (2), the functional layer (3) representing less than 20% of the volume of the dose (1), the functional layer (3) forming the shell of a body of revolution about the axis of symmetry of the dose (1) and the distance from the functional layer (3) to the axis of symmetry being variable.
6. A process for the production of an axisymmetrical multilayer dose as claimed in any one of claims 1 to 4, comprising a step in which the distance from the functional layer (3) to the axis of symmetry of the dose (1) is varied, said process consisting in coextruding a multilayer rod or tube of resins in the molten state, then in periodically cutting said rod or said tube in the molten state, said step being carried out by periodically varying the flow rate of at least one layer, the periodicity of the flow rate being equal to the periodicity of the cutting.
7. The process as claimed in claim 6, characterized in that the flow rate of two layers varies periodically and in phase opposition.
8. A process for the production of an axisymmetrical multilayer dose as claimed in any one of claims 1 to 4, comprising a step in which the distance from the functional layer (3) to the axis of symmetry of the dose (1) is varied, said process consisting in injecting, into the cavity of a mold, a plurality of resins (2, 3) in the molten state, at least one of which is a functional resin (3), the injection of the functional layer (3) being preceded and followed by the injection of at least one resin (2), then in ejecting the dose (1) in the molten state from the cavity of said mold, and in varying the volume of the cavity proportionally to the volume of resin injected.

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